1. Technical Field of the Invention
The present invention relates to component mounting method and apparatus wherein a component is mounted on a mounting surface by bonding their respective metallic electrical bonding interconnects. In particular, it describes the process of and apparatus for manufacturing an electronic circuit substrate wherein electronic components such as bare IC chips are mounted on substrates such as printed-wiring circuit boards.
2. Description of Prior Art
Bare IC chips are formed of a semiconductor wafer on which circuit patterns are fabricated using thin-film forming techniques and mounted on a printed board for manufacturing an electronic circuit board. As shown in FIG. 11, electrodes 107 are prefabricated in a circuit pattern on a bare IC chip 103 to be electrically connected to conductor lands 109 formed on a printed-wiring board 104. For mounting such bare IC chip 103 on the circuit board 104, a surface mount method is used wherein the bonding face 103a of the IC chip 103 where the electrodes 7 exist and the bonding face 104a of the circuit board 104 where the conductor lands 109 exist are brought to a face-to-face contact and fixed to each other for achieving electrical connection between the conductor lands 109 and electrodes 107. Sealant 111 made of resin is then filled between the bonding faces 103a, 104a as shown in FIG. 12 for encapsulating the circuit pattern including the electrical bonding areas formed on the bonding face 103a of the IC chip 103.
In a mounting method which has been used in recent years, a bare IC chip 103, on which metal bumps 108 have been formed upon electrodes 107 as shown in FIG. 11 by a wire bonding process or the like, is held by suction with a suction nozzle 114 and is brought opposite to a circuit board 104 at a predetermined location, where the bumps 108 are pressed onto conductor lands 109 on the circuit board 104 for bonding them in electrical connection with each other. At the same time the bumps 108 and conductor lands 109 are fixed to each other with adhesive 112 that may be supplied in advance to bumps 108 or conductor lands 109 or with solder paste that assists electrical bonding of metal interconnects. The bare IC chip 103 is thus mounted on the circuit board 104. The circuit board 104 is then held in an inclined state as shown in FIG. 12, and sealant 111 is flowed between the bonding faces 103a, 104a of the IC chip 103 and circuit board 104 as shown in phantom lines in the figure with the use of a dispenser 115 or the like. Sealing is completed when the sealant 111 is filled between the IC chip 103 and circuit board 104 as shown in solid lines in FIG. 12.
In such method the equipment cost is high, since the process of mounting bare IC chips 103 on circuit boards 104 and the process of dispensing sealant 111 between the bonding faces 103, 104a of IC chip 103 and circuit board 104 differ substantially from each other in the handling of circuit boards and the design of operations, and are performed separately in different apparatuses. Moreover, the sealant 111 takes time to flow into between the bonding faces 103, 104a, wherefore the productivity is low. For example, in the case of mounting an IC chip 103 of 10mmxc3x9710mm size, the dispenser 115 is moved along the upper side of the IC chip from one end to another and returned so as to apply the sealant 111 to the entire area between the bonding faces 103a, 104a. The operation is finished only when the sealant has filled between IC chip 103 and circuit board 104 to the extent that a wetted portion 113 is formed around the IC chip 103 as shown in FIG. 12. In such method it takes about 10 seconds for the operation of mounting one IC chip 103. Furthermore, there is not much choice of sealing materials, i.e., the sealant 111 must have a viscosity in the range 2000 to 3000 cps, since it is poured into the very small gap of about 50 xcexcm between the bonding faces 103a, 104a. Moreover, a sealant 111 having such viscosity needs to be heated at a relatively high temperature of from 40 to 60xc2x0 C. to set, because of which the operation time is further increased. It is also undesirable in the interest of economy in energy since heat consumption is high.
In addition, there is a risk that fillers contained in the sealant 111 that is poured in between the bonding faces 103a, 104a may be distributed in stripes, causing a sealing failure. Also, since electrical connection between bumps 108 of IC chips 103 and conductor lands 109 of circuit boards 104 is accomplished only by mutual contact, a defective bond is sometimes formed, even though the electrical bonding areas on IC chips and circuit boards are fixed with each other with adhesive 112 and sealant 111. The yield of product is thereby decreased. The bumps 108 and lands 109 may be fixed with each other using solder paste, which will, however, result in consumption of more heat and time for heating solder paste and for letting it set.
An object of the present invention is to provide a method and an apparatus for mounting components in which electrical bonding of components on a mounting surface is achieved without failure in a short period of time with simple equipment and low heat consumption.
To accomplish the above object, the component mounting method according to the present invention comprises the steps of: supplying a sealant to one or both of the component and mounting surface; placing the component in proximity to the mounting surface; pressing an electrical bonding area of the component tightly to an electrical bonding area of the mounting surface, whereby the sealant is compressed and filled between the component and mounting surface in a required area; and generating friction between the electrical bonding areas of the component and the mounting surface in tight contact with each other by moving the component and mounting surface relative to each other, whereby both of the electrical bonding areas are melted and welded together.
By the above method, the sealant can be forcibly and instantaneously filled in a required area between the component and mounting surface without any additional operation or time. Therefore, the bonding of both electrical bonding areas and the filling of the sealant can be achieved with one operation in a short time. There are no viscosity restrictions on the sealant as in the case of the flowing method and a sealant of high viscosity can be used, wherefore the sealant can be set in a short time at a low temperature during the above operation. The component mounting can thus be accomplished with simple operation and apparatus in a short period of time with low heat consumption. Moreover, the electrical bonding areas are securely welded together by melting metal, whereby the formation of a defective bond is prevented and the yield is improved. The production cost can be accordingly reduced.
In particular, when pressure-welding the electrical bonding areas of the component and mounting surface by friction therebetween, the metal welding can be swiftly performed if ultrasonic vibration is applied to the component thereby ultrasonically bonding the electrical bonding areas.
The sealant is supplied in advance to at least one of the bonding faces of the component and mounting surface. Since it is provided in a mass, air is hardly mixed therein. Alternatively, the sealant may be coated using a dispenser, printed, or transferred at an appropriate time. Either way, the sealant can be fed simply and swiftly during or in association with the operations for handling the component or mounting surface.
By using a bump for at least one of the electrical bonding areas of the component and the mounting surface, the ultrasonic bonding of the local electrical bonding areas of the component and mounting surface can be achieved easily and securely with a sufficient amount of metal and without being interfered by other elements.
In order to achieve the above objects, the component mounting apparatus of the present invention comprises a component feeding section for feeding components to a predetermined location; a mounting surface handling device for handling and positioning a mounting surface at a predetermined location for component mounting and for transferring the mounting surface to other places; a component handling device having a component handling tool for picking up the component fed from the component feeding section, bringing a bonding face of the component into tight contact with a bonding face of the mounting surface, and pressing the component onto the mounting surface; an ultrasonic vibration device for applying ultrasonic vibration to the component held by the component handling tool through this tool; and a controller, wherein the controller performs controlling of the above sections and devices such that a metallic electrical bonding area of the component is located to face a metallic electrical bonding area of the mounting surface at the component mounting position, and both are tightly pressed to each other, so that a sealant that is supplied in advance to one of the bonding faces of the component and the mounting surface is compressed and filled between both bonding faces in a required area, and at the same time the ultrasonic vibration device is activated so as to ultrasonically bond the electrical bonding areas of the component and the mounting surface together. With the above apparatus, the above described method can be automatically implemented stably at a high speed by the control of the controller in accordance with a predetermined program.
By providing a sealant feeder for supplying the sealant to one of the bonding faces of the component and the mounting surface before the component and the mounting surface are located to face each other, the sealant feeder being activated by the controller, a single apparatus can automatically perform the component mounting operation including the process of supplying sealant to one of the component and mounting surface.
The application conditions of sealant fed by the sealant feeder may be varied by means of the controller in accordance with the type of component to be mounted. In this way the sealant can be applied in a suitable amount and in a favorable condition for various types of components that differ from each other in terms of the size of their bonding faces, and sealing conditions that may vary depending on the types of component can also be automatically varied. The type of component being mounted can be recognized by any of manually inputted component data, component data stored in mounting program data, and component data read from the component being fed or its support member.
By providing a detector for detecting the amount of sealant from the information obtained by recognizing images of the sealant filled between the component and mounting surface, the amount of sealant fed from the sealant feeder can be corrected by the controller in accordance with the detected amount of sealant. In this way, even if the amount of sealant in a predetermined condition increases or decreases for some unknown reasons, it can be corrected automatically so that favorite sealing is constantly achieved.
The mounting surface handling device feeds the mounting surface such that its bonding face is upwards for mounting operation, whereas the component feeding section feeds the component with its bonding face upwards where the electrical bonding area exists, and the component handling device comprises a flipping device which picks up the component from above and turns the component handling tool so that the bonding face of the component faces down, and a bonding device equipped with the ultrasonic vibration device, which picks up the component from above of which bonding face has been turned upside down and feeds the component for the ultrasonic bonding operation on the mounting surface at the component mounting position. Components that are fed with their active faces upwards such as bare IC chips can be mounted in order on a mounting surface that also faces upwards by such actions of the flipping device and bonding device cooperating with each other.
The sealant can be cured simply by being left, but if a heater for heating the sealant directly or indirectly is provided at least at the component mounting position, the setting of the sealant can be forcibly completed at the same time when the bonding of the component on the mounting surface is finished. Instead of heating by a heater, the sealant may also be cured using light such as ultraviolet.